The invention concerns equipment and automatic systems for electro-plating on metal sheets especially for the production of printed circuits.
To apply a protective or antioxidant film to the sheets or in any case a film designed to improve their quality, the sheets are immersed in a special bath. The components of the bath cause chemical reactions on the metal surface, especially on copper, producing a film of what is known as chemical tin, or chemical copper as the case may be, or other products.
For large-scale production specially devised mechanical means of transport pass the sheets through the bath one after another.
The procedure, based on a chemical reaction associated to the action of gravity, obviously takes considerable time partly because of the need to obtain an even film.
Purpose of the above invention is to shorten working times while ensuring optimum formation of the film on the sheets as will now be explained. Subject of the invention is a device, in a plant for electoplating a film on metal sheets, especially for printed circuits, translating continuously, parallel one to another, using special transporting means.
This device presents, in succession, one or more operative units each comprising one or more pairs of metal rollers, here called contact rollers, carrying along in axial rotation by mechanical means, reciprocally in the opposite direction, sealed oblong chambers, placed above the trajectory of the translating sheets, having a series of tubular nozzles with coplanar axes substantially side by side and parallel, provided with an internal oblong laminar electrode, a pump that continuously takes up a special liquid product recycled from a bath underneath and pumps it under pressure into said chambers, the device being connected to an electric-electronic drive unit which, in accordance with a specially devised program, controls and operates the movement of said rollers, action of the pump, translation of the sheets and generation of direct electric current.
Said pairs of rollers and said chambers are placed transversally to the direction of translation of the sheets.
The electrode inside the sealed chamber and said contact rollers are reciprocally electrically insulated and respectively connected to the two poles of said direct current.
As the sheets pass between the pairs of contact rollers the liquid pumped into the chamber is projected through the nozzles onto the areas of the sheets while these emerge from said rollers.
It follows that, due to the effect produced by closure of the electric circuit generated by the DC current between the liquid and the sheets, these latter become electro-plated as desired.
After the pair of contact rollers and before the oblong chamber, bearing in mind the direction of movement, each operative unit comprises, in succession, a first pair of rollers, here called containment rollers, resting laterally one above another and drawn along in axial rotation, reciprocally opposingly directed, by mechanical means.
The upper roller is surrounded by a number of substantially equal rings placed side by side, whose internal diameter is considerably larger than the diameter of said upper roller.
Associated to said first oblong chamber with tubular nozzles is a second oblong chamber opposite to the first and placed below the trajectory of the translating sheets.
Said second chamber is substantially similar to the first one but, instead of tubular nozzles, it has a nozzle with a narrow longitudinal slit in it substantially opposite to the set of nozzles of the chamber above and extending to the same length as that of said set.
The second chamber is also supplied by the pump with recycled liquid from the bath below, and has inside it a laminar oblong electrode connected to the same electric pole to which the electrode of the first chamber is connected.
After said pair of chambers there is a second pair of containment rollers substantially equal to the first pair.
The upper chamber is placed higher than the upper rollers comprised in the two pairs of containment rollers.
The lower chamber is placed lower than the axis of the lower rollers of said two pairs of containment rollers.
The level and reciprocal distance of the longitudinal edges of the upper faces of said lower chambers are such as will ensure contact between the surfaces of said lower rollers and said edges thus forming a kind of intermediate channel comprising a base, formed of the upper face of said lower chambers, and sides formed of the opposite surfaces of said lower rollers forming the two pairs of containment rollers.
Said channel therefore becomes filled with the liquid that emerges under pressure through the slit nozzle for the lower chambers.
When the rings of the upper rollers in said pairs of containment rollers spontaneously rest on the surfaces of the advancing sheets, they sub stantially form a channel whose base is formed by the advancing sheets and whose side walls are formed by the external surfaces of said rings.
This channel too fills up with active liquid from the nozzles of said upper chambers.
Each operative unit advantageously comprises, between the pairs of contact and containment rollers, a freely turning pair of rollers here called finishing rollers.
The rollers of each pair are respectively served by supports formed of rectangular recesses made in the opposite sides of the framework of the installation into which recesses the pins and cylindrical extensions to the two ends of said rollers can fit.
Due to its own weight, therefore, the upper roller of each pair of rollers bears on the lower roller and consequently on the metal sheets when they pass between said rollers.
The mechanism that rotates the pair of contact rollers comprises gear wheels fixed to the ends of the lower rollers of the pair, said gears meshing with a continuous chain placed orthogonally to said rollers and driven by an electric motor.
The rollers of each pair are linked by substantially similar gear wheels.
Even though the upper roller in the pair of contact rollers is slightly separated from the lower one by passage of the metal sheets, its rotation is assured by the length of the teeth of the gear wheels, these being considerably longer than the thickness of said sheets.
The mechanism that causes rotation of the pair of containment rollers comprises helical gear wheels fixed to the opposite ends (in relation to the ends of the contact rollers) of the lower rollers in the pair, these gears meshing with the helical gear wheels fixed to a motor driven shaft orthogonal to said rollers.
The two rollers of each pair are linked by substantially equal helical gear wheels.
The contact rollers and the laminar electrodes placed inside the sealed chambers are respectively connected electrically to the negative and positive poles of the direct current.
Should it be required to have electro-plating on oblong sheets with raised edges of plastic material, the contact finishing and containment rollers are made with annular bands, of a width corresponding to that of said oblong sheets, between said edges and projecting above the height of said edges on both faces of said sheets.
The dimensions of the rings round the containment rollers and of the internal and external diameters, as well as width, are calculated to allow them to settle spontaneously both on the faces of the sheets and on the raised edges.
The film may be of chemical tin or of chemical copper or may possess other characteristics.
The contact rollers are advantageously of titanium.
The finishing and containment rollers and the rings round said latter rollers are advantageously of plastic material.
The invention offers evident advantages. By closure of the direct current electric circuit between the active liquid, receiving a polarity from the electrodes in the sealed chambers with nozzles, and the sheets receiving the second polarity from the titanium rollers, deposition times of the particles in the liquid and of the chemical reactions that form the film on both faces of the sheets are greatly accelerated.
All this is accompanied by a reduction in the costs of manufacturing printed circuits especially, and by a considerable improvement in quality.
Characteristics and purposes of the disclosure will be made still clearer by the following examples of its execution illustrated by diagrammatically drawn figures.